In recent years, display devices that are excellent in visibility and have low power consumption are required. Display devices that emit light or modulate light from a self light-emitting body such as CRTs (Cathode Ray Tubes), PDPs (Plasma Display Panels), and LCDs (Liquid Crystal Displays), which are commonly used in these days, are bright and easy to see but have a problem of large power consumption.
From the view point of low power consumption, it is preferable that a display device has a memory property, with which the screen which is once displayed is maintained without power, and it is further preferable that the drive voltage is low.
In recent years, as the display device having such properties, electrodeposition display devices (hereinafter, referred to as “ED devices”) that contain electrolysis solution containing metal or compound having metal in its chemical structure, or electrochemical display devices (hereinafter, referred to as “ECDs”) employing the reversible change of light absorption state due to oxidation-reduction reaction on the electrode are being actively developed.
The ED device and the ECD utilize, in a display principle, the change in light absorption in reacting substance itself due to oxidation-reduction reaction on the electrode, and these elements are more advantageous in terms of cost reduction and process reduction than the LCD since they do not need such members as polarizers or backlights.
As a method for manufacturing an ED device and an ECD, the vacuum injection method, which was used for manufacturing conventional LCDs, was used at first. However, recently, the vacuum bonding method used for manufacturing large LCDs is broadly used to deal with larger display panels and to improve display property such as display non-uniformity after long-term use, because it is difficult to inject electrolysis solution by the conventional vacuum injection method in order to use gel or highly-viscous electrolysis solution.
A schematic flow of the vacuum bonding method used in manufacturing LCDs are shown in FIGS. 7a and 7b, and a seal pattern 105 is formed on a lower substrate 101 with UV (ultra violet) curable seal material 103, for example (see FIGS. 7a-7d), and a moderate amount of display material 107 made of liquid crystal is dispensed with a dispenser inside the seal pattern 105 (see FIG. 7b). On the surface of the lower substrate 101 on which the seal pattern 105 is to be formed, there is a lower electrode (not shown in the drawing) previously formed.
After that, the lower substrate 101 is decompressed as a whole in a vacuum chamber, and an upper substrate 201 is stacked on the lower substrate 101 in the decompressed environment (see FIG. 7c). On the surface, of the upper substrate 201, which is facing the lower substrate 101, there is an upper electrode (not sown in the drawing) previously formed. By stacking, the display material 107 dispensed with the dispenser is spread inside the seal pattern 105. Next, by opening the vacuum chamber to the atmosphere, the upper substrate 201 is uniformly pressed as a whole by the atmospheric pressure. After that, the seal material 103 is cured by the exposure of UV light to adhere the upper substrate 201 and the lower substrate 101, thereby an LCD panel 1 is completed (FIG. 7d).
However, the electrolysis solution used as the display material for the ED device and the ECD contains solvent, and the solvent is more likely to volatilize than the liquid crystal material. In the vacuum bonding method for the above-described manufacture of the LCD, there is a step for decompressing the lower substrate on which the liquid crystal material has been dispensed, in the vacuum chamber before the stacking, and in the case of the ED device and the ECD, the solvent component of the electrolysis solution volatilizes under the reduced-pressure.
The electrolysis solution to be dispensed is adjusted in its composition to display appropriately, and volatilization of a part of the composition causes change in the composition rate, thereby degrading display quality. Further, due to volatilization of a part of the composition, the surface of the electrolysis solution is dried, and traces of dispense and unevenness of injection of the electrolysis solution appear when the display panel is completed, thereby resulting in deterioration in the display quality.
To address this issue, as a manufacturing method of a display panel using display material with high volatility, Patent Document 1, for example, discloses a method in which display material of more amount than needed for filling up one panel is dispensed, and bonding is performed while ejecting gas bubbles from the edge of the upper substrate. In addition, Patent Document 2 discloses a manufacturing method of a display panel in which stacking is performed while controlling the degree of vacuum of the depression according to a formula.